Mosgate driver integrated circuit with adaptive dead time

ABSTRACT

An IGBT device, comprising a substrate having a conductivity type; a drain electrode arranged on a bottom surface of the substrate; an epitaxial layer arranged on the substrate and having a conductivity type opposite that of the substrate; at least one body diffusion arranged within the epitaxial layer and having a conductivity type the same as that of the substrate; at least one source diffusion arranged within the body diffusion and having a conductivity type the same as that of the epitaxial layer; a gate electrode to control the IGBT device; a source electrode electrically coupled to the body diffusion and the source diffusion; an additional diffusion arranged within the epitaxial layer and having a conductivity type the same as that of the substrate, the additional diffusion forming a collector region of a vertical bipolar arrangement in the IGBT; and a sense electrode electrically coupled to the additional diffusion; wherein the presence of minority carriers in the epitaxial layer may be detected in accordance with a voltage of the sense electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/456,686, filed Jun. 5, 2003 in the name of InternationalRectifier Corporation and entitled MOSGATE DRIVER INTEGRATED CIRCUITWITH ADAPTIVE DEAD TIME.

FIELD OF THE INVENTION

This invention relates to driver circuits for gated switching devices,for example, a MOSgate driver circuit for driving first and secondseries connected MOS-gated devices.

BACKGROUND OF THE INVENTION

With respect to various applications (e.g., integrated circuitapplications), it is known to employ driver circuits for driving atleast two gated switches, for example, at least two gated power switchesand/or power MOSgated devices (e.g., MOSFETs, IGBTs, GTO Thyristors,etc.). Referring now to FIG. 1, there is seen an exemplary MOS-gatedcircuit 100 according to the prior art. MOS-gated circuit 100 includesfirst and second gated switches 115, 120 electrically coupled to oneanother in series, as well as a driver circuit 105 configured to controlthe conduction states of gated switches 115, 120 via respective gateoutput signals 125, 130, such that only one of gated switches 115, 120conducts at any given time. Such circuits are commonly used, forexample, in bridge legs of rectifiers for buck converters and the like.

Referring now to FIG. 2, there is seen an exemplary timing diagramshowing the turn-on and turn-off times of respective gate output signals125, 130 for the conventional MOS-gate driver circuit of FIG. 1.Respective output signals 125, 130 are controlled in anti-phase, suchthat only one of gated switches 115, 120 conducts at any given time.

In actual applications, however, gated switches 115, 120 may beincapable of immediately switching from a conductive state to anon-conductive state in response to respective output signals 125, 130.That is, inherent gate capacitances may result in associated turn-offdelay times, during which gated switches 115, 120 remain conductiveafter receiving turn-off commands from driver circuit 105. Thus, theideal “anti-phase” control may not prevent simultaneous conduction ofgated switches 115, 120. As such, it is known to intentionally provide a“dead-time” after turning off either of gated switches 115, 120, thedead-time being larger than the longest turn off delay of gated switches115, 120 (e.g., between 1 and 3 μS). During this dead-time, neither ofgated switches 115, 120 is controlled to conduct, as shown in FIG. 2.

Although these measures may prevent simultaneous conduction of gatedswitches 115, 120, the additional dead-time reduces the maximum dutycycle and the modulation depth of the Pulse Width Modulated (PWM)control of gated switches 115, 120. For example, with respect to acarrier frequency of 20 khz (Period=50 μS) and a 3 μS dead-time, themaximum duty cycle is:1−3/50=94%.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a MOS-gated drivercircuit capable of overcoming the disadvantages of prior art drivercircuits described above. For this purpose, the present inventionproposes a MOS-gated circuit capable of automatically controlling thedead-time in a closed loop to prevent the simultaneous conduction of theMOS-gated switches, such as MOSFETs or IGBTs. The dead-timedetermination is based on the status of each switch (e.g., the abilityof each switch to withstand a reverse voltage before the other switchcan turn on). In this manner, the shortest possible dead-time can beautomatically provided. Any desired characteristic may be monitored, forexample, threshold voltage, to determine when the MOS-gated device iscapable of withstanding a reapplied voltage.

In one exemplary embodiment, an adaptive dead time circuit is providedfor first and second series connected MOS-gated devices configured toconduct sequentially, but not simultaneously. The circuit includes firstand second monitor circuits coupled to the MOS-gated devices configuredto produce respective output signals in response to the measurement of acharacteristic of the first and/or second MOS-gated devices related totheir ability to withstand a reverse voltage. The output signals of thefirst and second monitor circuits are respectively connected to the gateelectrodes of the MOS-gated devices to enable their turn on in responseto an output signal from said first and second monitor circuits,respectively; whereby simultaneous conduction of the first and secondMOS-gated devices is prevented and the dead-time between theirconduction sequences is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a driver circuit according to the prior art.

FIG. 2 is a timing diagram showing anti-phase control of the drivercircuit of FIG. 1.

FIG. 3 is a timing diagram showing anti-phase control of an exemplaryMOS-gated circuit according to the present invention.

FIG. 4 shows an exemplary MOS-gated circuit according to the presentinvention.

FIG. 5 shows a variant of the exemplary MOS-gated circuit of FIG. 4.

FIG. 6 shows an exemplary IGBT switch according to the present inventionincluding a sense electrode for detecting minority carriers.

FIG. 7 shows an exemplary IGBT driver circuit according to the presentinvention for controlling a plurality of IGBT.

DETAILED DESCRIPTION

Referring now to FIG. 4, there is seen an exemplary MOS-gated circuit400 according to the present invention. MOS-gated circuit 400 includes abridge leg 410 (or other circuit component) having first and secondgated switches 415, 420 electrically coupled to one another in series,as well as a driver circuit 405 for controlling the conduction state ofgated switches 415, 420. For this purpose, driver circuit 405 generatesrespective output signals 425, 430, which are controlled in accordancewith high-side and low-side control inputs 426, 431 to control theconduction states of gated switches 415, 420, respectively.

Although FIG. 4 shows a MOS-gated circuit 400 configured to control theconduction states of two gated switches 415, 420 of bridge leg 410, itshould be appreciated that MOS-gated circuit 400 may be employed tocontrol any number of gated switches in any configuration, such as, forexample, four gated switches in an H-bridge configuration.

To prevent simultaneous conduction of gated switches 415, 420, drivercircuit 405 includes first and second conduction detect circuits 435,440 respectively assigned to each of gated switches 415, 420. Conductiondetect circuits 435, 440 are configured to generate conduction detectsignals 445, 450 in accordance with whether their associated gatedswitches 415, 420 are capable of sustaining a reapplied voltage withoutconducting. Each conduction detect signal 445, 450 forms one input of arespective AND-logic component 455, 460, with the other input beingformed by a respective one of high-side and low-side control inputs 426,431. In this manner, if a selected one of gated switches 415, 420 is notcapable of sustaining a reapplied voltage without conducting, theconduction detect circuit 435, 440 assigned to that switch 415, 420prevents the other one of switches 415, 420 from conducting. That is,conduction detect circuits 435, 440 automatically produce appropriatedead-times to prevent simultaneous conduction of gated switches 415,420, as shown in the timing diagram of FIG. 3.

By providing conduction detect circuits 435, 440 in accordance with thepresent invention, a circuit designer need not precisely calculate theworst case dead time, since detect circuits 435, 440 self-adjust to theconduction characteristics of gated switches 415, 420. In this manner,it may be better ensured that gated switches 415, 420 operate with theminimum dead time.

Referring now to FIG. 5, there is seen another exemplary MOS-gatedcircuit 500, in which the conduction detect circuits 435, 440 includerespective comparators 505, 510 configured to produce output signals inaccordance with the difference between the gate-to-source voltage oftheir assigned switch 415, 420 and a reference voltage (V_(REF)), whichmay be selected to be at or below the threshold voltages of switches415, 420. For this purpose, the positive inputs of comparators 505, 510are connected to the gates of their respectively assigned gated switches415, 420, and the negative inputs of comparators 505, 510 are connectedto reference voltage (V_(REF)). In this manner, each of comparators 505,510 produces its output signal in accordance with whether its assignedswitch 415, 420 is capable of sustaining a reapplied voltage withoutconducting.

The various exemplary embodiments of the present invention describedabove may be applied to driver circuits operable to control IGBTswitches. However, since IGBT switches are minority carrier devices, ittakes time for minority carriers in the epitaxial layer of the IGBTs todecay after turn-off. As such, detecting whether the gate-to-sourcevoltage of an IGBT is below a predetermined reference voltage may notguarantee that an IGBT switch is capable of sustaining a reappliedvoltage without conducting.

Referring now to FIG. 6, there is seen an exemplary IGBT switch 600according to the present invention capable of permitting externalcircuitry to detect the presence of minority carriers in the epitaxiallayer of the IGBT switch. As is known, IGBT switch 600 includes a Psubstrate 605, upon which is grown an—epitaxial layer 610, P doped bodydiffusions 615 a, 615 b, N+ diffusions 620 a, 620 b, 620 c, 620 d, agate electrode 625, a source electrode 630, and a drain electrode 635 onthe bottom surface of P substrate 605. However, unlike the prior art,IGBT switch 600 includes an additional P diffusion 640 (e.g., aP-diffusion 640 for N type IGBT 600) according to the present invention.The additional P diffusion forms the collector of a vertical bipolardevice 645 (e.g., a PNP bipolar transistor 645 in N type IGBT 600), witha sense electrode 650 being electrically coupled to the additional Pdiffusion (collector) 640. In this manner, the presence of minoritycarriers in the—epitaxial layer may be detected by measuring the voltagedrop across the sense electrode 650 and the drain electrode 635, therebyproviding a more reliable measure as to whether the IGBT 600 is capableof sustaining reapplied voltage without conducting.

Referring now to FIG. 7, there is seen an exemplary IGBT driver circuit700 according to the present invention for controlling at least one IGBTswitch of FIG. 6. IGBT driver circuit 700 includes a bridge leg 710having first and second IGBT switches 715, 720 electrically coupled toone another in series, as well as a driver circuit 705 for controllingIGBT switches 715, 720. Similar to the exemplary embodiments describedabove, driver circuit 705 is configured to control the conduction statesof IGBT switches 715, 720 via respective output signals 725, 730, whichare controlled in accordance with high-side and low-side control inputs726, 731 for controlling the conduction states of IGBT switches 715,720, respectively.

To prevent simultaneous conduction of IGBT switches 715, 720, drivercircuit 405 includes first and second conduction detect circuits 735,740 respectively assigned to each of IGBT switches 715, 720. Conductiondetect circuits 735, 740 are configured to generate conduction detectsignals 445, 450 in accordance with whether their associated gatedswitches 415, 420 are capable of sustaining a reapplied voltage withoutconducting. For this purpose, detect circuits 735, 740 measure thevoltage across the sense electrodes 750, 755 and drain electrodes 760,765 of there respectively assigned IGBT switches 715, 720. In thismanner, if a selected one of IGBT switches 715, 720 is not capable ofsustaining a reapplied voltage without conducting, the conduction detectcircuit 735, 740 assigned to that switch 715, 720 prevents the other oneof switches 715, 720 from conducting.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein.

1. An IGBT device, comprising: a substrate having a conductivity type; adrain electrode arranged on a bottom surface of the substrate; anepitaxial layer arranged on the substrate and having a conductivity typeopposite that of the substrate; at least one body diffusion arrangedwithin the epitaxial layer and having a conductivity type the same asthat of the substrate; at least one source diffusion arranged within thebody diffusion and having a conductivity type the same as that of theepitaxial layer; a gate electrode to control the IGBT device; a sourceelectrode electrically coupled to the body diffusion and the sourcediffusion; an additional diffusion arranged within the epitaxial layerand having a conductivity type the same as that of the substrate, theadditional diffusion forming a collector region of a vertical bipolararrangement in the IGBT; and a sense electrode electrically coupled tothe additional diffusion; wherein the presence of minority carriers inthe epitaxial layer may be detected in accordance with a voltage of thesense electrode.